The invention presented herein relates to a laser scanning apparatus for the production of high resolution microfilm images from electronic data signals such as are available from raster image based electronic image storage systems and, in particular, to such a laser scanning apparatus wherein a resonant scanner is used and a grating clock is utilized to linearize the resonant scanning.
The grating clock approach, which includes the use of a line grating plate with a phase lock loop, has been used for many high resolution laser scanning systems wherein the output resolution is required on the order of 400 dots/centimeter to 4000 dots/centimeter. Examples are laser phototypesetters, high quality business graphic printers, graphic arts recorders and laser publication printers. The grating clock provides synchronization between the scan line movement of the laser beam at the surface of the recording media and the data clock across the entire scan line for excellent linearization of the image along the scan line. This excellent linearization is particularly appreciated when the laser beam is directed to the recording media via a resonant galvanometric mirror wherein the mirror movement is sinusoidal. The gratings as used in the prior art laser scanning systems provide no other function.
There is need in laser scanning apparatus for the production of high resolution microfilm images of engineering drawings of various sizes to provide accurate sizing of the microfilm images so that a copy produced from such microfilm will be the proper size relative to the scale used for the microfilmed engineering drawing. In addition, it is desirable that the images for various standard size engineering drawing be centered within the film presented for imaging via a laser scanner apparatus.